swift3.0->String类中的API变化

   Swift版的Cocoa框架中的API有了大范围的修改外，Swift的一些核心库也有了很大的改动。其中字符串类型String在方法API上更加简洁，其中变动较大的是与下标相关的方法，列举如下：

var string = "Hello-Swift"

//获取某个下标后一个下标对应的字符 char="e"

var char = string[string.index(after: startIndex)]

//获取某个下标前一个下标对应的字符 char2 = "t"

var char2 = string[string.index(before: string.endIndex)]

//通过范围获取字符串中的一个子串 Hello

var subString = string[startIndex...string.index(startIndex, offsetBy: 4)]

var subString2 = string[string.index(endIndex, offsetBy: -5)..<endIndex]

//获取某个子串在父串中的范围

var range = string.range(of: "Hello")

//追加字符串操作 此时string = "Hello-Swift! Hello-World"

string.append(" Hello-World")

//在指定位置插入一个字符 此时string = "Hello-Swift!~ Hello-World"

string.insert("~", at: string.index(string.startIndex, offsetBy: 12))

//在指定位置插入一组字符 此时string = "Hello-Swift!~~~~ Hello-World"

string.insert(contentsOf: ["~","~","~"], at: string.index(string.startIndex, offsetBy: 12))

//在指定范围替换一个字符串 此时string = "Hi-Swift!~~~~ Hello-World"

string.replaceSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 4), with: "Hi")

//在指定位置删除一个字符 此时string = "Hi-Swift!~~~~ Hello-Worl"

string.remove(at: string.index(before:string.endIndex))

//删除指定范围的字符 此时string = "Swift!~~~~ Hello-Worl"

string.removeSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 2))

var string2 = "My name is Jaki"

//全部转换为大写

string2 = string2.uppercased()

//全部转换为小写

string2 = string2.lowercased()